1. Field of the Invention
This invention relates to an improvement of a variable speed pulley type speed-shifting device utilizing a belt drive in motor cycles, agricultural implements, and the like.
2. Description of the Prior Art
Conventionally, as a variable speed pulley type speed-shifting device utilizing belt drive a well known device, for example, composes a pair of an input and output shafts placed parallely, variable speed pulleys composed of fixed sideplates solidly rotatably and axially non-slidably mounted to each shaft and movable sideplates solidly rotatably and axially slidably mounted on each shaft forming V-shaped belt grooves with the fixed sideplates facing thereto, and a belt member trained to the belt grooves between both sideplates, arranged so that the transmission ratio between the shafts is adjusted in the manner that the effective radius of the pulleys for the belt member is changed by moving axially the movable sideplates of each pulley toward and away from the fixed sideplates. Usually, working of the above-mentioned movable sideplates of each pulley is controlled by utilizing hydraulic equipment. Nevertheless, in the case utilizing the hydraulic equipment, a piping system for the hydraulic equipment is required. Also, there are problems that the control of the working of the movable sideplates is complicated, and the device needs a large space.
A device in which the movable sideplates of variable pulleys may be automatically operated, for example, is disclosed in published Japanese application No. 59-62760 in which is provided a pair of transmission shafts, male screw cylinders axially non-slidably and rotatably mounted to the transmission shafts, female screw cylinders solidly movable in the axial direction and rotatably mounted to the movable sideplates of variable speed pulleys on the transmission shafts engaged with guide grooves of supporting flanges of the male screw cylinder with a certain play, arranged so as to adjust the effective radius of the pulleys by changing the distance between the fixed sideplates and the movable sideplates of the variable speed pulleys by screw motion of rotating the male screw cylinders to move the female screw cylinders by a servomotor adapted as an actuator.
However, this proposed device has a problem that controlling for operation of the servomotor and the construction of the device is complicated since the movable sideplates of the pulleys are working by screw motion in order to move the female screw cylinder by an output of the servomotor. Also, the cost is high since installing the servomotor is expensive.
This invention has been made in view of the above disadvantages and its object is to provide a speed-shifting device wherein the working of the movable sideplates is easy to control with a simple, durable and low cost arrangement by moving the sideplate by utilizing the rotational power of the transmission shaft effectively.